805=533MHz FSB, 8x0 is all 800FSB. Runs at 2.66 stock, meaning 20x multiplier. Good deal, should overclock well from what I've been reading. As for the board, ATI's RS400 chipsets supports DDR1 and DDR2- just not simultaneously.
That Sempron combo is a hot deal. I picked up that deal about a month ago, and I overclocked that Sempron from 1800 mhz to 2250 on that ECS board, just by raising the FSB to 250 in the bios (running divider on ram). I also picked up 1 gig of Corsair value ram for $49 after rebate too. My wife likes her new rig.